An imaging device, such as a printing device, typically has an AC to DC power supply to power the various components of the device. For example, a printing device has a print cartridge with a printhead to apply an imaging medium to a print media. The printhead has one or more pens that are turned on and off to apply the imaging medium to the print media. Pen turn-on energy is closely controlled in a printing device in an effort to ensure high-quality printouts. Some of the variables of pen turn-on energy include an operating temperature, how long a pen has been in service, and manufacturing variations and tolerances. Variations in the power supply output voltage can affect the pen turn-on energy which can result in a degradation of print quality or a shorter printhead life.